1. Field of The Invention
This invention is related to tongs, and particularly to tong load cell assemblies and methods of their use.
2. Description Of Related Art
In virtually every industrial field there is at least some requirement for assembling and disassembling members having mating threaded connections such as, pipe, rods and bolts. Perhaps the best known requirement for making-up (or breaking-out) of such members exists in the well drilling and servicing industries, particularly that involving exploration for, and production of, oil and gas wells. In the oil and gas field, depending on the phase of operations being conducted, miles of drill pipe, hole casing or production tubing are necessarily assembled at the surface on a piece-by-piece basis. Similarly, each time it becomes necessary to remove pipe, casing or tubing from the borehole (for bit changes, pipe repair, pipe salvage or many other reasons), the string of pipe is progressively lifted from the hole, and disassembled at the surface on a piece-by-piece basis. Because of the need to repetitively make and break threaded member connections, various apparatus, generally referred to as tongs, more specifically lead tongs and back-up tongs, have been developed to facilitate that task. In each make-up of a joint of two threaded members a specific torque should be applied. Some means is used to "hold" the tongs "in place", that is, restrain them from rotating about the pipe axis during tightening or loosening, usually by snubbing lines or by means interconnecting the tongs.
When a lead tong is operated, a rotary element contained within the tong body grasps a first threaded member. A motor, usually hydraulic, contained within the lead tong body generates a "driving torque" which is applied to the rotary element to rotate it, and the first threaded member therein, in the desired direction. By operation of Newton's third law of physics (that is, in essence, "for every force there exists an equal and opposite force"), creation of the "driving torque" (which is applied to the threaded member) results in a "reaction torque", which is applied to the lead tong body in the opposite direction. This reaction torque must be counteracted, to secure the lead tong body from spinning about the pipe rather than driving the pipe itself.
When manual tongs were used an upper tong was conventionally interconnected by a cable and torque gauge to a powered winch, and a lower tong was connected oppositely thereof through a cable to a point of anchorage on the drilling rig. When the winch was activated, the connecting cable would turn the so-called "pipe tongs" to rotate the upper joint until the torque gauge registered the torque considered to effect a fluid-tight seal, (during make-up of the drill string) or to break the threaded connection in the case of disassembly of the drill string. The snubbing cable attached to the lower tong would, of course, secure the lower tong and thus the box portion of the lower joint of drill pipe from rotation during this process.
When a back-up tong is used with a lead power tong, it is advantageous to ascertain the relative torque between the two units during operation hence some degree of mutual freedom between the two tongs permits a relative torque measurement to be made therebetween. To assure mechanical integrity of a joint and its leak tightness, it is desirable to measure the torque used to make-up a joint.
In a typical situation, the two tongs are interconnected by a framework or mounting apparatus and two tension load cells, one load cell on each side of the assembly provides tensile load readings when the tongs are operated for joint make-up or break out. Alternatively, one load cell is employed and is switched from one side of the assembly to the other as needed, always measuring a tensile load.
A variety of load cells are commercially available, including hydraulic load cells and tension links. Load cells are available that read in both tension and compression but they are relatively expensive; have specific associated electronic devices and software; may be difficult to calibrate; and often provide lower measurement resolution. These disadvantages outweigh the benefits that can be obtained by using only one such load cell.
In accordance with 37 C.F.R. .sctn.1.56 the following are disclosed:
U.S. Pat. No. 4,972,741 discloses a tong apparatus and discusses the measurement of tong torque with typical load cells.
U.S. Pat. No. 4,957,177 discloses a dual beam moment-insensitive load cell.
U.S. Pat. No. 4,402,239 discloses a tong and a torque gauge interconnected between a tong and a snubbing cable and a typical torque sensor.
U.S. Pat. No. 4,401,000, commonly owned with the present invention, discloses a power tong.
U.S. Pat. No. 4,290,304 discloses a back-up tong and a power tong used together and the use of typical load cells with a "stinger" assembly or arm which acts against a load cell.
U.S. Pat. No. 4,246,809 discloses a tong apparatus with a lead tong and a back-up tong.
U.S. Pat. No. 4,125,040, commonly owned with this invention, discloses tong control apparatus that uses typical strain gauges or the like in a back-up line and transducers.
U.S. Pat. No. 4,082,017 discloses power tong apparatus including an upper and a lower tong.
"General Services and Products Catalog 1988-89," Weatherford discloses a variety of tongs (pages 26-30), tong services (pages 8, 9, 15) and a load cell device (page 13).
"Speedtork Hydraulic Drilling Tongs," Weatherford, 1990 discloses a tong assembly using two load cells.
"Dillon Bulletin #100.2" W. C. Dillon & Co., Inc., 1982 discloses load cells.
"Dillon Bulletin #500.1," W. C. Dillon & Co., Inc., 1982 discloses strain gage load cells.
There has long been a need for an easy and efficient way to ascertain tong torque measurements. There has long been a need to reduce the need for using two tension-indicating load cells when using a lead and a back-up tong.